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Immune system deficiencies in SAM
International Congress Series 1260 (2004) 41 – 46
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Immune system deficiencies in SAM Tomohide Hosokawa * Department of Life Science, Kyoto University of Education, 1 Fukakusa-Fujinomori-cho, Fushimi, Kyoto 612-8522, Japan Received 8 July 2003; accepted 4 September 2003
Abstract. The immune system in SAMP strains shows signs of early senescence in various functional aspects. Interestingly, cultured spleen cells from mice of SAMP strains with the major histocompatibility complex (MHC) haplotype of H-2k showed an impaired antibody production against xenogenic red blood cells, indicating that SAMP strains of mice have some immune system deficiencies. Here, we selected SAMP1 strain with H-2k to investigate further the immune system deficiencies in SAMP strains. The following new aspects of the immune system deficiencies have been reported. (1) Cultured spleen cells of SAMP1 mice also show an impaired antibody production against a protein antigen. (2) The antibody-forming system in SAMP1 mice has a defect in the pathways that respond to the regulatory stimuli from the neuroendocrine system. (3) Splenic CD4+ T cells from young SAMP1 mice show abnormally short-lasting production of IL-2 in response to mitogenic stimulus, leading to the impaired proliferation and survival of these cells. The short-lasting IL-2 production may limit propagation of antigen-specific T cells and reduce the magnitude of the ongoing immune response. (4) After stress-induced atrophy, young SAMP1 thymus shows abnormally low regenerative activity, resulting from extremely poor lymphocyte proliferation in it. This may lead to the early decline in the thymus function with aging. D 2003 Elsevier B.V. All rights reserved. Keywords: Th1; Th2; Noradrenaline; Corticosterone; Thymus atrophy; SAMP1
1. Introduction Inbred strains of mice termed SAM were developed by Takeda et al. [1]. These strains consist of short-lived, accelerated senescence-prone (SAMP) and long-lived, accelerated senescence-resistant (SAMR) strains. SAMP strains of mice are basically healthy and grow normally, but show signs of early senescence in various tissues and organs. Various functional aspects of the immune system in SAMP strains also show early signs of senescence. The principal findings regarding early immunosenescence in the SAMP strains are summarized in Table 1.
* Tel.: +81-75-644-8278; fax: +81-75-645-1734. E-mail address: [email protected] (T. Hosokawa). 0531-5131/ D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0531-5131(03)01565-6
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Table 1 Principal findings of the early immunosenescence and the immune defects in SAMP strains Early senescence or defects in immune functions
Reference number
In vitro antibody production against sheep red cells In vivo antibody production against sheep red cells NK activity In vivo DTH response Mitogen-induced production of IL-2 Antigen-presenting cell function Autoimmune abnormalities
[2,8] [3,11] [2,8,12] [3] [4,8,25] [5] [6]
Previous studies have shown that the immune system in SAMP strains shows an ageassociated early decline in antibody production, natural killer (NK) cell activity, and the delayed type hypersensitivity (DTH) response [2,3]. The SAMP strains have also been reported to show an early age-associated decline in the mitogen-induced productions of interleukin-2 (IL-2) and IL-4 [4] and in the antigen-presenting cell (APC) function of B cells and dendritic cells [5]. Age-associated autoimmune abnormalities in SAMP1 mice have also been reported [6]. Importantly, the SAMP strains with the major histocompatibility complex (MHC) haplotype of H-2k, which account for almost all SAMP strains, show a profound defect in the in vitro antibody response to a T-dependent antigen, xenogenic red blood cells, as early as 2 months of age [2,7,8]. This extremely low in vitro antibody response was attributed to impaired T helper-2 (Th2) cell activity [7] and seemed to be controlled by several genes [9,10]. Interestingly, the defect was also controlled epigenetically by environmental conditions, since it was apparent when mice were reared under conventional conditions but not under specific pathogen-free (SPF) environments [11]. Dong et al. [12] reported that young SAMP1 mice showed impaired NK cell and virusspecific cytotoxic T lymphocyte activity in spite of producing appropriate amounts of influenza virus-specific antibody when the mice were challenged with live influenza viruses. Dong et al. suggested that SAMP1 mice had a partial deficiency of Th1 cells and normal Th2 cell activity. Their suggestion is apparently inconsistent with our argument that SAMP strains of mice with H-2k show impaired Th2 cell activity in response to the in vitro challenge with xenogenic red blood cells. Although xenogenic red blood cells induce a primary antibody-forming response in cultured spleen cells, the response does not seem to be a typical T-dependent antibody response. Thus, we used the protein OVA as a typical T-dependent antigen in order to reinvestigate the impaired antibody response of SAMP1 cells. 2. Reinvestigation of the defective in vitro antibody response to T-dependent antigen in SAMP1 mice SAMP1 and C3H/He mice were immunized with one or two intraperitoneal injections of OVA with alum adjuvant. Spleen cells from immunized and unprimed mice were cultured with OVA for 14 days. The results indicated that OVA-specific IgG and IgA antibody responses were induced by the addition of OVA to cultures when the C3H/He donor mice were immunized with two OVA injections. However, the antibody response of
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Table 2 IFN-g and IL-4 production of cultured spleen cells from OVA-primed SAMP1 and C3H/He mice Strain
OVA in culture
IFN-g
IL-4 (mean F SE, pg/ml)
SAMP1
no 0.1 Ag/ml no 0.1 Ag/ml
479 F 433 879 F 455 <5 62 F 18*
272 F 18 387 F 46 66 F 10 219 F 9*
C3H/He
* P < 0.05 vs. C3H no OVA.
the spleen cells from SAMP1 mice receiving the same priming procedure was much lower than that of the C3H/He cells [13], clearly indicating that the cultured SAMP1 spleen cells showed an impaired antibody response against T-dependent antigens. Depletion of adherent cells from the OVA-primed C3H/He spleen cells markedly reduced the OVA-specific antibody responses, which were almost completely restored by adding peritoneal adherent cells from either C3H/He or SAMP1 mice to the culture [13]. Thus, the antigen-presenting function of adherent cells from SAMP1 mice is normal in young mice. Taken together, these observations strongly suggest that SAMP strains of mice have an impairment in the Th2 cell response to T-dependent antigens. Furthermore, the OVA-primed SAMP1 donor mice showed significantly lower antiOVA IgG production in the peripheral blood than the OVA-primed C3H/He donor mice at day 7 after the first immunization [13]. A similar low in vivo antibody response of the SAMP1 mice was observed when mice were immunized with suboptimal doses of xenogenic red blood cells [11]. Therefore, we argue that the impaired Th2 cell activity, which is obviously observed in the cell culture system, is also apparent in the early phase of the primary antibody response when the SAMP1 mice are immunized by T-dependent antigens under suboptimal conditions. The defect may be circumvented at a later phase of the primary antibody response in cases where the SAMP1 mice are immunized by antigens, such as proteins with alum adjuvant or live microorganisms, which stimulate the immune system continuously to recruit undifferentiated immature T cells. Next, we measured the production of the Th1 cytokine, interferon (IFN)-g, and the Th2 cytokine, IL-4, in spleen cells to further investigate impaired Th2 cell activity in SAMP1 mice. SAMP1 and C3H/He mice were immunized with a single intraperitoneal injection of OVA with alum adjuvant. We selected alum since it is a potent inducer of Th2-type immune responses. When cultured with OVA, the OVA-primed SAMP1 spleen cells produced a substantial amount of both IL-4 and IFN-g regardless of the presence or absence of OVA in the culture. Thus, cytokine production appeared to be antigennonspecific. In contrast, the OVA-primed C3H/He spleen cells produced IL-4 and IFN-g in response to OVA in the culture, although the amount of IFN-g was less than that in the SAMP1 cell cultures (Table 2). These results also indicate impaired Th2 cell activity in SAMP1 mice. 3. Modulation of T-helper cell functions of SAMP1 by neuroendocrine stimuli The central nervous system (CNS) and the immune system interact closely with each other [14,15]. The interaction of these two systems is essential for maintaining homeostasis of the mammalian body. The CNS affects the immune system via two major
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pathways, the hypothalamic – sympathetic nervous system axis and the hypothalamic – pituitary – adrenal axis. Stress in mammals stimulates the two pathways to secrete catecholamines and stress hormones, which suppress the immune system. However, a neurotransmitter of sympathetic nerves, noradrenaline (NA), augments the antibodyforming responses under certain conditions [16 – 18]. Accordingly, we investigated whether the SAMP1 immune system was regulated effectively via the two pathways to correct the low antibody responsiveness against T-dependent antigens. Noradrenaline (NA) and corticosterone (CS) were selected as neuroendocrine stimuli since they are the major effector molecules secreted from sympathetic nerve endings and the adrenal cortex, respectively, during stress in mice. SAMP1 and C3H/He mice were immunized with two intraperitoneal injections of OVA with alum adjuvant. Spleen cells primed with OVA were then cultured with OVA in the presence of varying concentrations of NA or CS [19]. NA showed significant dosedependent regulatory effects on the response of the C3H/He spleen cells, the anti-OVA antibody production was augmented at a concentration of 3.0 10 5 M and suppressed at a concentration of 3.0 10 4 M, respectively. In contrast, NA at the concentrations tested, had little effect on the antibody response of SAMP1 spleen cells. Furthermore, CS suppressed the antibody response of the C3H/He spleen cells in a dose-dependent manner at concentrations between 1.0 10 7 and 1.0 10 5 M. In contrast, the antibody response of the SAMP1 spleen cells was not significantly altered by the same concentrations of CS. These results suggest that the Th2-dependent antibody-forming system in SAMP1 mice has some defect in the pathways that respond to NA and CS. Next, we investigated whether NA affects the production of IFN-g and IL-4 in the OVA-primed spleen cells [20]. SAMP1 and C3H/He mice were immunized with a single intraperitoneal injection of OVA with alum adjuvant. NA showed significant dosedependent regulatory effects on the production of IL-4, but not IFN-g, in the C3H/He spleen cells, the cytokine production was augmented at a concentration of 3.0 10 5 M and suppressed at a concentration of 3.0 10 4 M, respectively. In contrast, NA did not augment but did suppress the IL-4 production of the SAMP1 spleen cells dose dependently at concentrations higher than 3.0 10 5 M. The IFN-g production of spleen cells from either strain of mice were not affected by NA at any of the concentrations tested. NA seems to augment the IL-4 production of OVA-specific Th2 cells in the C3H/ He spleen cell culture indirectly via enhancing the release of Th2-promoting cytokines by APCs [21,22], since Th2 cells are reported to express no h2-adrenergic receptors [23]. At any rate, the OVA-specific IL-4 producing machinery in the SAMP1 spleen cells showed no response to the upregulating stimulus of NA. 4. Abilities of the SAMP1 immune system to supply T cells and to propagate antigen-specific T cells: insight into the immune system deficiencies of SAMP1 mice Aging causes a progressive atrophy of the thymus, leading to an age-associated decline in various T cell functions. Stress also induces thymus atrophy, although this is usually transient. Accordingly, we compared the ability of the thymus to recover from stress-caused atrophy between young SAMP1 and age-matched C3H/He mice [24]. Stress, which caused a slight reduction in the thymus weight, decreased lymphocyte
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populations in the thymus of both strains. The thymic lymphocyte population in C3H/He mice started to recover at 24 h after stress treatment. In clear contrast, the lymphocyte population in the SAMP1 thymus did not recover but continued to decrease until 7 days after the treatment, being progressively replaced by fibroblasts. These results suggest that the regenerative mechanisms of the SAMP1 thymus, the microenvironment for proliferation and maturation of the thymic lymphocytes or the thymic lymphocytes themselves, have some defects. The low regenerative activity of the thymus may supply an inadequate number of T cells, leading to the accelerated aging of various immune activities in SAMP1 mice. Recently, Nishimura et al. [25] found that splenic CD4+ T cells from young SAMP1 mice show abnormally short-lasting production of IL-2 in response to stimulation with concanavalin A, leading to the impaired proliferation and survival of these cells. The short-lasting IL-2 production and resulting insufficient production of IL-2 may limit propagation of antigen-specific T cells in the ongoing immune response, reducing the magnitude of the immune response. The abnormal IL-2 production may accelerate further age-associated declines in the T cell-dependent immune activity, when the supply of new and naive T cells is limited because of accelerated thymus aging. 5. Conclusions (1) The antibody-forming system in young SAMP1 mice has a defect in the pathways that respond to the regulatory stimuli from the neuroendocrine system. (2) Splenic CD4+ T cells from young SAMP1 mice show abnormally short-lasting production of IL-2 in response to mitogenic stimulus, leading to the impaired proliferation and survival of these cells. The short-lasting IL-2 production may limit propagation of antigen-specific T cells and reduce the magnitude of the ongoing immune response. (3) After stress-induced atrophy, young SAMP1 thymus shows abnormally low regenerative activity, resulting from extremely poor lymphocyte proliferation in it. This may lead to the early decline in the thymus function with aging. SAMP strains with H-2k probably share with these immune system deficiencies in SAMP1, which seem to accelerate age-associated decline in the T cell-dependent immune functions in these mice. References [1] T. Takeda, M. Hosokawa, S. Takeshita, et al., A new murine model of accelerated senescence, Mech. Ageing Dev. 17 (1981) 183 – 194. [2] T. Hosokawa, M. Hosono, K. Higuchi, et al., Immune responses in newly developed short-lived SAM mice: I. Age-associated early decline in immune activities of cultured spleen cells, Immunology 62 (1987) 419 – 423. [3] E. Toichi, K. Hanada, T. Hosokawa, et al., Age-related decline in humoral immunity caused by the selective loss of TH cells and decline in cellular immunity caused by the impaired migration of inflammatory cells without a loss of TDTH cells in SAMP1 mice, Mech. Ageing Dev. 99 (1997) 199 – 217. [4] K. Aoki, K. Asano, K. Okamoto, et al., Age-related changes in ConA-induced cytokine production by splenocytes from senescence-accelerated mice SAMP8, Immunol. Lett. 46 (1995) 169 – 175. [5] H. Haruna, M. Inaba, K. Inaba, et al., Abnormalities of B cells and dendritic cells in SAMP1 mice, Eur. J. Immunol. 25 (1995) 1319 – 1325. [6] H. Yoshioka, H. Yoshida, T. Doi, et al., Autoimmune abnormalities in a murine model of accelerated senescence, Clin. Exp. Immunol. 75 (1989) 129 – 135.
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[7] T. Hosokawa, M. Hosono, K. Hanada, et al., Immune responses in newly developed short-lived SAM mice: II. Selectively impaired T-helper cell activity in in vitro antibody response, Immunology 62 (1987) 425 – 429. [8] Y. Abe, M. Yuasa, Y. Kajiwara, et al., Defects of immune cells in the senescence-accelerated mouse: a model for learning and memory deficits in the aged, Cell. Immunol. 157 (1994) 59 – 69. [9] K. Hanada, M. Hosono, T. Hosokawa, et al., Immune responses in newly developed short-lived SAM mice: III. Genetic control of defective helper T-cell activity in in vitro primary antibody response, Immunology 68 (1989) 540 – 546. [10] K. Hanada, H. Katoh, T. Hosokawa, et al., Immune responses in newly developed short-lived SAM mice: IV. Chromosomal location of a gene controlling defective helper T-cell activity, Immunology 74 (1991) 160 – 164. [11] M. Hosono, K. Hanada, E. Toichi, et al., Immune abnormality in relation to nonimmune diseases in SAM mice, Exp. Gerontol. 32 (1997) 181 – 195. [12] L. Dong, I. Mori, M. Jaber, et al., The senescence-accelerated mouse shows aging-related defects in cellular but not humoral immunity against influenza virus infection, J. Infect. Dis. 182 (2000) 391 – 396. [13] T. Kimura, A. Kohdan, T. Hosokawa, Antibody-forming response of cultured spleen cells to a protein antigen: function of antigen-presenting cells in SAMP1, in: Y. Nomura (Ed.), International Congress Series, vol. 1260, Elsevier, Amsterdam, 2004, pp. 209 – 213 (this volume). [14] J.E. Blalock, K.L. Bost (Eds.), Neuroimmunoendocrinology, Karger, Basel, 1988. [15] I.J. Elenokov, R.L. Wilder, G.P. Chrousos, et al., The sympathetic nerve—an integrative interface between two supersystems: the brain and the immune system, Pharmacol. Rev. 52 (2000) 595 – 638. [16] K. Kasahara, S. Tanaka, T. Ito, et al., Suppression of the primary immune response by chemical sympathectomy, Res. Commun. Pathol. Pharmacol. 16 (1977) 687 – 694. [17] V.M. Sanders, A.E. Munson, Beta adrenoceptor mediation of the enhancing effect of norepinephrine on the murine primary antibody response in vitro, J. Pharmacol. Exp. Ther. 230 (1984) 183 – 192. [18] R.J. Cross, J.C. Jackson, W.H. Brooks, et al., Neuroimmunomodulation: impairment of humoral immune responsiveness by 6-hydroxydopamine treatment, Immunology 57 (1986) 145 – 152. [19] M. Kitamura, Y. Yagi, T. Hosokawa, Regulatory effects of noradrenaline and corticosterone on the antibody-forming response of cultured spleen cells from SAMP1 mice, in: Y. Nomura (Ed.), International Congress Series, vol. 1260, Elsevier, Amsterdam, 2004, pp. 203 – 207 (this volume). [20] S. Hashimoto, R. Naruse, T. Hosokawa, Regulatory effects of noradrenalin on the production of Th1 and Th2 cytokines by cultured spleen cells in SAMP1 mice, in: Y. Nomura (Ed.), International Congress Series, vol. 1260, Elsevier, Amsterdam, 2004, pp. 215 – 219 (this volume). [21] I.J. Blenkov, D.A. Papanicolaou, R.L. Wilder, et al., Modulatory effects of glucocorticoids and catecholamines on human interleukin-12 and interleukin-10 production: clinical implications, Proc. Assoc. Am. Physicians 108 (1996) 374 – 381. [22] G.J. Maestroni, Short exposure of maturing, bone marrow-derived dendritic cells to norepinephrine: impact on kinetics of cytokine production and Th development, J. Neuroimmunol. 129 (2002) 106 – 114. [23] D.S. Ramer-Quinn, R.A. Baker, V.M. Sanders, Activated T helper 1 and T helper 2 cells differentially express the B2-adrenergic receptor, J. Immunol. 159 (1997) 4857 – 4867. [24] M.S. Miyamoto, Y. Miyamoto, T. Hosokawa, Morphological changes of the thymus under stress caused by water immersion and restraint in SAMP1 mice, in: Y. Nomura (Ed.), International Congress Series, vol. 1260, Elsevier, Amsterdam, 2004, pp. 199 – 202 (this volume). [25] Y. Nishimura, T. Hosokawa, M. Hosono, et al., Insufficient interleukin-2 production from splenic CD4+ T cells causes impaired cell proliferation and early apoptosis in SAMP1, a strain of senescence-accelerated mouse, Immunology 107 (2002) 190 – 198.
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Immune system deficiencies in SAM Tomohide Hosokawa * Department of Life Science, Kyoto University of Education, 1 Fukakusa-Fujinomori-cho, Fushimi, Kyoto 612-8522, Japan Received 8 July 2003; accepted 4 September 2003
Abstract. The immune system in SAMP strains shows signs of early senescence in various functional aspects. Interestingly, cultured spleen cells from mice of SAMP strains with the major histocompatibility complex (MHC) haplotype of H-2k showed an impaired antibody production against xenogenic red blood cells, indicating that SAMP strains of mice have some immune system deficiencies. Here, we selected SAMP1 strain with H-2k to investigate further the immune system deficiencies in SAMP strains. The following new aspects of the immune system deficiencies have been reported. (1) Cultured spleen cells of SAMP1 mice also show an impaired antibody production against a protein antigen. (2) The antibody-forming system in SAMP1 mice has a defect in the pathways that respond to the regulatory stimuli from the neuroendocrine system. (3) Splenic CD4+ T cells from young SAMP1 mice show abnormally short-lasting production of IL-2 in response to mitogenic stimulus, leading to the impaired proliferation and survival of these cells. The short-lasting IL-2 production may limit propagation of antigen-specific T cells and reduce the magnitude of the ongoing immune response. (4) After stress-induced atrophy, young SAMP1 thymus shows abnormally low regenerative activity, resulting from extremely poor lymphocyte proliferation in it. This may lead to the early decline in the thymus function with aging. D 2003 Elsevier B.V. All rights reserved. Keywords: Th1; Th2; Noradrenaline; Corticosterone; Thymus atrophy; SAMP1
1. Introduction Inbred strains of mice termed SAM were developed by Takeda et al. [1]. These strains consist of short-lived, accelerated senescence-prone (SAMP) and long-lived, accelerated senescence-resistant (SAMR) strains. SAMP strains of mice are basically healthy and grow normally, but show signs of early senescence in various tissues and organs. Various functional aspects of the immune system in SAMP strains also show early signs of senescence. The principal findings regarding early immunosenescence in the SAMP strains are summarized in Table 1.
* Tel.: +81-75-644-8278; fax: +81-75-645-1734. E-mail address: [email protected] (T. Hosokawa). 0531-5131/ D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0531-5131(03)01565-6
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T. Hosokawa / International Congress Series 1260 (2004) 41–46
Table 1 Principal findings of the early immunosenescence and the immune defects in SAMP strains Early senescence or defects in immune functions
Reference number
In vitro antibody production against sheep red cells In vivo antibody production against sheep red cells NK activity In vivo DTH response Mitogen-induced production of IL-2 Antigen-presenting cell function Autoimmune abnormalities
[2,8] [3,11] [2,8,12] [3] [4,8,25] [5] [6]
Previous studies have shown that the immune system in SAMP strains shows an ageassociated early decline in antibody production, natural killer (NK) cell activity, and the delayed type hypersensitivity (DTH) response [2,3]. The SAMP strains have also been reported to show an early age-associated decline in the mitogen-induced productions of interleukin-2 (IL-2) and IL-4 [4] and in the antigen-presenting cell (APC) function of B cells and dendritic cells [5]. Age-associated autoimmune abnormalities in SAMP1 mice have also been reported [6]. Importantly, the SAMP strains with the major histocompatibility complex (MHC) haplotype of H-2k, which account for almost all SAMP strains, show a profound defect in the in vitro antibody response to a T-dependent antigen, xenogenic red blood cells, as early as 2 months of age [2,7,8]. This extremely low in vitro antibody response was attributed to impaired T helper-2 (Th2) cell activity [7] and seemed to be controlled by several genes [9,10]. Interestingly, the defect was also controlled epigenetically by environmental conditions, since it was apparent when mice were reared under conventional conditions but not under specific pathogen-free (SPF) environments [11]. Dong et al. [12] reported that young SAMP1 mice showed impaired NK cell and virusspecific cytotoxic T lymphocyte activity in spite of producing appropriate amounts of influenza virus-specific antibody when the mice were challenged with live influenza viruses. Dong et al. suggested that SAMP1 mice had a partial deficiency of Th1 cells and normal Th2 cell activity. Their suggestion is apparently inconsistent with our argument that SAMP strains of mice with H-2k show impaired Th2 cell activity in response to the in vitro challenge with xenogenic red blood cells. Although xenogenic red blood cells induce a primary antibody-forming response in cultured spleen cells, the response does not seem to be a typical T-dependent antibody response. Thus, we used the protein OVA as a typical T-dependent antigen in order to reinvestigate the impaired antibody response of SAMP1 cells. 2. Reinvestigation of the defective in vitro antibody response to T-dependent antigen in SAMP1 mice SAMP1 and C3H/He mice were immunized with one or two intraperitoneal injections of OVA with alum adjuvant. Spleen cells from immunized and unprimed mice were cultured with OVA for 14 days. The results indicated that OVA-specific IgG and IgA antibody responses were induced by the addition of OVA to cultures when the C3H/He donor mice were immunized with two OVA injections. However, the antibody response of
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Table 2 IFN-g and IL-4 production of cultured spleen cells from OVA-primed SAMP1 and C3H/He mice Strain
OVA in culture
IFN-g
IL-4 (mean F SE, pg/ml)
SAMP1
no 0.1 Ag/ml no 0.1 Ag/ml
479 F 433 879 F 455 <5 62 F 18*
272 F 18 387 F 46 66 F 10 219 F 9*
C3H/He
* P < 0.05 vs. C3H no OVA.
the spleen cells from SAMP1 mice receiving the same priming procedure was much lower than that of the C3H/He cells [13], clearly indicating that the cultured SAMP1 spleen cells showed an impaired antibody response against T-dependent antigens. Depletion of adherent cells from the OVA-primed C3H/He spleen cells markedly reduced the OVA-specific antibody responses, which were almost completely restored by adding peritoneal adherent cells from either C3H/He or SAMP1 mice to the culture [13]. Thus, the antigen-presenting function of adherent cells from SAMP1 mice is normal in young mice. Taken together, these observations strongly suggest that SAMP strains of mice have an impairment in the Th2 cell response to T-dependent antigens. Furthermore, the OVA-primed SAMP1 donor mice showed significantly lower antiOVA IgG production in the peripheral blood than the OVA-primed C3H/He donor mice at day 7 after the first immunization [13]. A similar low in vivo antibody response of the SAMP1 mice was observed when mice were immunized with suboptimal doses of xenogenic red blood cells [11]. Therefore, we argue that the impaired Th2 cell activity, which is obviously observed in the cell culture system, is also apparent in the early phase of the primary antibody response when the SAMP1 mice are immunized by T-dependent antigens under suboptimal conditions. The defect may be circumvented at a later phase of the primary antibody response in cases where the SAMP1 mice are immunized by antigens, such as proteins with alum adjuvant or live microorganisms, which stimulate the immune system continuously to recruit undifferentiated immature T cells. Next, we measured the production of the Th1 cytokine, interferon (IFN)-g, and the Th2 cytokine, IL-4, in spleen cells to further investigate impaired Th2 cell activity in SAMP1 mice. SAMP1 and C3H/He mice were immunized with a single intraperitoneal injection of OVA with alum adjuvant. We selected alum since it is a potent inducer of Th2-type immune responses. When cultured with OVA, the OVA-primed SAMP1 spleen cells produced a substantial amount of both IL-4 and IFN-g regardless of the presence or absence of OVA in the culture. Thus, cytokine production appeared to be antigennonspecific. In contrast, the OVA-primed C3H/He spleen cells produced IL-4 and IFN-g in response to OVA in the culture, although the amount of IFN-g was less than that in the SAMP1 cell cultures (Table 2). These results also indicate impaired Th2 cell activity in SAMP1 mice. 3. Modulation of T-helper cell functions of SAMP1 by neuroendocrine stimuli The central nervous system (CNS) and the immune system interact closely with each other [14,15]. The interaction of these two systems is essential for maintaining homeostasis of the mammalian body. The CNS affects the immune system via two major
44
T. Hosokawa / International Congress Series 1260 (2004) 41–46
pathways, the hypothalamic – sympathetic nervous system axis and the hypothalamic – pituitary – adrenal axis. Stress in mammals stimulates the two pathways to secrete catecholamines and stress hormones, which suppress the immune system. However, a neurotransmitter of sympathetic nerves, noradrenaline (NA), augments the antibodyforming responses under certain conditions [16 – 18]. Accordingly, we investigated whether the SAMP1 immune system was regulated effectively via the two pathways to correct the low antibody responsiveness against T-dependent antigens. Noradrenaline (NA) and corticosterone (CS) were selected as neuroendocrine stimuli since they are the major effector molecules secreted from sympathetic nerve endings and the adrenal cortex, respectively, during stress in mice. SAMP1 and C3H/He mice were immunized with two intraperitoneal injections of OVA with alum adjuvant. Spleen cells primed with OVA were then cultured with OVA in the presence of varying concentrations of NA or CS [19]. NA showed significant dosedependent regulatory effects on the response of the C3H/He spleen cells, the anti-OVA antibody production was augmented at a concentration of 3.0 10 5 M and suppressed at a concentration of 3.0 10 4 M, respectively. In contrast, NA at the concentrations tested, had little effect on the antibody response of SAMP1 spleen cells. Furthermore, CS suppressed the antibody response of the C3H/He spleen cells in a dose-dependent manner at concentrations between 1.0 10 7 and 1.0 10 5 M. In contrast, the antibody response of the SAMP1 spleen cells was not significantly altered by the same concentrations of CS. These results suggest that the Th2-dependent antibody-forming system in SAMP1 mice has some defect in the pathways that respond to NA and CS. Next, we investigated whether NA affects the production of IFN-g and IL-4 in the OVA-primed spleen cells [20]. SAMP1 and C3H/He mice were immunized with a single intraperitoneal injection of OVA with alum adjuvant. NA showed significant dosedependent regulatory effects on the production of IL-4, but not IFN-g, in the C3H/He spleen cells, the cytokine production was augmented at a concentration of 3.0 10 5 M and suppressed at a concentration of 3.0 10 4 M, respectively. In contrast, NA did not augment but did suppress the IL-4 production of the SAMP1 spleen cells dose dependently at concentrations higher than 3.0 10 5 M. The IFN-g production of spleen cells from either strain of mice were not affected by NA at any of the concentrations tested. NA seems to augment the IL-4 production of OVA-specific Th2 cells in the C3H/ He spleen cell culture indirectly via enhancing the release of Th2-promoting cytokines by APCs [21,22], since Th2 cells are reported to express no h2-adrenergic receptors [23]. At any rate, the OVA-specific IL-4 producing machinery in the SAMP1 spleen cells showed no response to the upregulating stimulus of NA. 4. Abilities of the SAMP1 immune system to supply T cells and to propagate antigen-specific T cells: insight into the immune system deficiencies of SAMP1 mice Aging causes a progressive atrophy of the thymus, leading to an age-associated decline in various T cell functions. Stress also induces thymus atrophy, although this is usually transient. Accordingly, we compared the ability of the thymus to recover from stress-caused atrophy between young SAMP1 and age-matched C3H/He mice [24]. Stress, which caused a slight reduction in the thymus weight, decreased lymphocyte
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populations in the thymus of both strains. The thymic lymphocyte population in C3H/He mice started to recover at 24 h after stress treatment. In clear contrast, the lymphocyte population in the SAMP1 thymus did not recover but continued to decrease until 7 days after the treatment, being progressively replaced by fibroblasts. These results suggest that the regenerative mechanisms of the SAMP1 thymus, the microenvironment for proliferation and maturation of the thymic lymphocytes or the thymic lymphocytes themselves, have some defects. The low regenerative activity of the thymus may supply an inadequate number of T cells, leading to the accelerated aging of various immune activities in SAMP1 mice. Recently, Nishimura et al. [25] found that splenic CD4+ T cells from young SAMP1 mice show abnormally short-lasting production of IL-2 in response to stimulation with concanavalin A, leading to the impaired proliferation and survival of these cells. The short-lasting IL-2 production and resulting insufficient production of IL-2 may limit propagation of antigen-specific T cells in the ongoing immune response, reducing the magnitude of the immune response. The abnormal IL-2 production may accelerate further age-associated declines in the T cell-dependent immune activity, when the supply of new and naive T cells is limited because of accelerated thymus aging. 5. Conclusions (1) The antibody-forming system in young SAMP1 mice has a defect in the pathways that respond to the regulatory stimuli from the neuroendocrine system. (2) Splenic CD4+ T cells from young SAMP1 mice show abnormally short-lasting production of IL-2 in response to mitogenic stimulus, leading to the impaired proliferation and survival of these cells. The short-lasting IL-2 production may limit propagation of antigen-specific T cells and reduce the magnitude of the ongoing immune response. (3) After stress-induced atrophy, young SAMP1 thymus shows abnormally low regenerative activity, resulting from extremely poor lymphocyte proliferation in it. This may lead to the early decline in the thymus function with aging. SAMP strains with H-2k probably share with these immune system deficiencies in SAMP1, which seem to accelerate age-associated decline in the T cell-dependent immune functions in these mice. References [1] T. Takeda, M. Hosokawa, S. Takeshita, et al., A new murine model of accelerated senescence, Mech. Ageing Dev. 17 (1981) 183 – 194. [2] T. Hosokawa, M. Hosono, K. Higuchi, et al., Immune responses in newly developed short-lived SAM mice: I. Age-associated early decline in immune activities of cultured spleen cells, Immunology 62 (1987) 419 – 423. [3] E. Toichi, K. Hanada, T. Hosokawa, et al., Age-related decline in humoral immunity caused by the selective loss of TH cells and decline in cellular immunity caused by the impaired migration of inflammatory cells without a loss of TDTH cells in SAMP1 mice, Mech. Ageing Dev. 99 (1997) 199 – 217. [4] K. Aoki, K. Asano, K. Okamoto, et al., Age-related changes in ConA-induced cytokine production by splenocytes from senescence-accelerated mice SAMP8, Immunol. Lett. 46 (1995) 169 – 175. [5] H. Haruna, M. Inaba, K. Inaba, et al., Abnormalities of B cells and dendritic cells in SAMP1 mice, Eur. J. Immunol. 25 (1995) 1319 – 1325. [6] H. Yoshioka, H. Yoshida, T. Doi, et al., Autoimmune abnormalities in a murine model of accelerated senescence, Clin. Exp. Immunol. 75 (1989) 129 – 135.
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